Meriva brakes

[Meriva22]

Does anyone know if there is a cover on the inside side of the brake disc on a Vauxhall Meriva?  I have a slight grinding sound when coming to a standstill and had the car to a local garage where the technician spent 30 seconds looking under the car whilst it was on the floor and said I needed new pads which I suspected.  The next day he’s then sent me a quote for a “brake rebuild” and claims I also need discs.  A friend who does his own car maintenance has checked over the car and say if it was his car wouldn’t change the discs as they have thousands more miles on them and that the technician couldn’t have checked the disc from the underside inside as there is a cover on it.  The cover does appear slightly rusty but my understanding is it’s a dust cover, is it an issue? 

[Vauxhall Owners Club]

The brakes do normally have a dust cover but if the discs are worn and fitting new pads will decrease the efficiency of the braking for a period.
If the cost is not too bad for the discs then maybe worth fitting at this stage